In 2007, DWP completed work to categorise the 76.8 million National Insurance numbers held on the DWP customer information system database for the UK.
Each number provides a unique numerical link between the individual and their National Insurance Contributions held on the HMRC National Insurance and Pay as you Earn Recording System. This was the most thorough and exhaustive analysis of these ever undertaken by DWP or
any of its predecessor organisations.
Some of the analysis has since been used in answer to Parliamentary Questions and is therefore already in the public domain. In the interests of transparency, the full results are published here.